The joining of annular work pieces together in end-to-end relationship, as in building pipe lines, is a highly technical procedure. Many have attempted to do this by automatic methods, or semi-automatic. Some have been successful but most have not. The rigid specifications required for girth joints in pipelines, as used for transmission of natural gas and petroleum products have made it difficult to accomplish by machinery. Hand welding or semi-automatic procedures have not been entirely satisfactory either and they are expensive.
While a recently developed system, as in U.S. Pat. No. 3,461,264, which starts with an internal "stringer bead" and completes the joint from the outside has been quite successful commercially, it would be preferable, if possible to weld the whole joint from the outside. Major difficulties encountered in attempts to weld from the outside often involve the control of penetration. Many proposals have been made to control penetration by use of back-up or internal chill members. These add to the complexity of apparatus and method and are not always useful because of misalignment of elements of pipe ends that are to be joined together.
The precise and careful preparation of the end surfaces to be joined is one important requirement for successful welding of girth joints in the field. In a shop, where heavy, massive equipment can be employed, quality joints can more readily be welded and preparatory end-shaping operations can more readily be carried out.
Notable advances in the field preparations of pipe ends for welding were realized when portable precision equipment such as in U.S. Pat. Nos. 3,608,406 and 3,733,933 was developed. The present invention involves further refinements to obtain better control of the flow of molten metal from the electric arc, especially when the initial welding pass is to be made from the outside of the pipe. A combination of machining and of cold rolling or swaging of the metal is found to be highly useful.